Just want to add my .02 on this K40 relay...I have a 2000 SLK that my daughter drives away at college...She called and states the car would have low power at times and the check engine light would come on at times...I'm in the automotive repair field and called the local MB repair shop for estimate of diagnosic after pulling the codes...They wanted $850 to $1500 because they stated by the time they got the car that far apart to find the issue...After joining SLKWorld and doing a search I found this wonderful article and inspected the car myself...15-20 minutes later I see the burnt soldier joints and resoldiered, fixed and the cost was zero!!!! Bazzle was right on... Codes were P1525, P1235, P1236, and P1420 in that order...

Thanks for the information regarding the K 40 relay. My 1999 SLK 230 lost power last week. I found your informative repair notes. I purchased a new K40 relay for $157.00 USD, installed it and the SLK is back in full power. Thanks!

Hi Guys, I am going to say that my SLK 230K 1998 has been in to Mercedes 3 times and they have had it over 2 weeks and in total i think i have spent well over £600 (lab and parts) to have this issue with intermittent starting and stopping fixed. First they said there was chafing of some cable on the undercarriage then changing the fuel pump. At no time have they mentioned this. I am furious. If i can find this on teh internet then why couldnt MB dealer (MB UK themselves) sort this out. It has been over 2 years and i have hardly driven the car 100 miles since (luckily it is a weekend or fun car). I am just about to see if i can repair this my self and if it is the problem, If it is i will be contacting MB and giving them a real earfull. Thank you Bazzle. I've had the car from new and its only done 32,000miles.

Well i have checked out the k40 relay circut board as per Bazzles instructions. The three little soldered bits in the corner look fine no degredation at all, cant see any anywhere else either so have not touched teh soldering iron. I gave it a good blow and cleaned the 40A fuse and put it back in. I have tried re-starting it but cant get it to turn over.

My symptoms are exactly as described by Millerpim on the other thread ->

2000 SLK Ignition Troubles & Died at Light
For the past several months, when I turn the key in the ignition to start the car, nothing happens. No noise. No engagement. After 2 or 3 tries, which involve removing the key and reinserting it, it will engage and start. Yesterday, I ended up cranking the key 50 times or more before it finally started. Today, it fired right up, but after driving for 20 minutes and sitting at a light, it suddenly died while in drive. I put it in park and tried to start it. It did not start. After a couple minutes of fidgeting with the key and turning it over and over, it finally started. What could cause this?

In addition my problem seems to be that if i turn the key to position 2, the fan comes on immediately (even on a cold start) and keeps spinning at high speed nothing else happens if i try and turn to ignition no sound of it trying to turn over or anything.

--------------------------------------
Prab again -------> So having had a look at the circuit board and it looking ok. Is there anything else anyone can reccomend. I have lost faith with the dealers and just want to get her up and running again. Sicne i took the module out she has not started again but that was only 30 mins ago will try her again later.

1) Sorry no idea how to read the codes on the car. Do i need to take it to MB for that? Would be great to do it though.

2) By the fan i mean the Fan behind the radiator grill (radiator fan i guess)- the big round one that sits between the engine and just behind the grill at the front of the car. The fans inside the car used to come on when it first used to stall whilst driving (if the vents were on). But now when it fails to start or when it does stop whilst driving it is just this big fan under the bonnet.

Did the fan go "crazy" after you checked the main board?
If so you should double check the connections. If the fan control (N76) http://www.buellwinkle.com/r170/comn76.htm doesn't get a signal when you turn on the igition the fan goes into a emergency mode. If connections ARE ok, you could have a problem with your AC control.

Thanks Gabus. Will take a look in teh morning is dark now. The fan has always gone crazy whenever the car suddenly stops or if i start it and it starts and stops or if it just does not turn over, eitehr way it suddenly comes on and teh fan keeps going. Then a few minutes or sometimes a day later i can start it and suddenly it works again for a while and then at some random time it all happens again.

The day i put the module back in it would not start at all (Coincidence i think) i could not see any broken solder it looked smooth and intact on the 3 connections mentioned by bazzle. But today 4 days later it suddenly started 6 times (i have not drvien it yet) and runs at standstill fine. Will take it out tommorow - fingers crossed. After i check the AC control N76.

ANy other ideas? Can i read the codes myself? How? Really need to get her out and make the most of the little sun we are likely to get this year.

Oh and also the roof is not folding down the switch lights up if i push in teh close direction but the open direction nothing happens no light flashing or anything? The car has not been drvien since last October. really should have taken her out more if it wasnt for this intermittent starting and driving problem. :-(

Thank you. I checked the N76 - The connections appear ok - not sure on each cable though but the main block that goes in seemed fine. The fan is still going crazy but sometimes i can start it ok and the fan is fine and then 10 minutes later or another time i can try and start it and nothing happens except the fan going at high speed behind the radiator grill.

How do i check the codes? And what would be the first thing to replace given the above or should i trust Mercedes Benz again with it (again).

Did the fan go "crazy" after you checked the main board?
If so you should double check the connections. If the fan control (N76) http://www.buellwinkle.com/r170/comn76.htm doesn't get a signal when you turn on the igition the fan goes into a emergency mode. If connections ARE ok, you could have a problem with your AC control.

I wanted to thank this thread! I was getting some codes, checked this thread... went in expecting to do some soldering and found out one of the 5 15 amp fuses had blown. I replaced it and ol' murky is back to her original prowess. No codes!!

I have a 1998 with 123,600 miles and suffer from the always on check engine light. I tried your method and thought it was going to work. Restarted the car and light went out, but the engine had a very bad miss. As I continued driving, the light went back on and the bad missing eventually went way, but when I floor the gas, it still hesitates quite a little. Dealer says that they can't read the comnputer and I get an "ERROR" when I try to read it with my device. I've been told I need a new computer mod, but I'm not sure I want to pay $1,700 plus labor for that fix. Can a used part be programmed to work with another car?

I just wanted to thank you for this very helpful thread. My car would die while driving for no reason every couple months and could not be duplicated. It finally would not crank yesterday and I found this thread today. This worked like champ! Thanks again

Hello and thank you for the pictures and the post. I own a 1999 SLK230, the car often would not turn over, no ignition...nothing. All electricals would work, lights, top, windows even the engine fan...but the car would not crank...dead....I removed the k40 and cleaned the 3 spots witch were just like the pictures, I also cleaned the 40 or 45amp fuse and put it all back, the car started right up. I will order a new k40 as a back up just incase...thanks again for the help

Looking at those joints, I would say it's not poor soldering (the board appears to have been wave soldered anyway), but the component on the otherside of it overheating. What is actually attached to those pads?

Hi all,
I am a new SLK owner. Had similar symptoms of others here. Engine cutting off in on hwy, and stopped at lights. Recently car wouldnt start at all, no crank, just radiator fan running on high speed. Pulled out K-40 and the solders dont look as bad as the ones pictured but I guess i can see some worn out frayed areas. My friend is going to resolder tomorrow. I hope this solves the issue but I'm not sure if this is the cause since the solders really dont look that bad. 1 question I have is: in bazzle's instructions it says "Remove old solder and resolder with new"....How does one remove the old solder?
Also, just wondering did anybody who posted that they were having these issues "Prabo, WeB, etc." ever come to a fix?
Any info grealy appreciated, ty.

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